The present invention relates to a coupling for the leak-free connection of pipe ends of pipes that are intended for transporting liquid and/or gaseous media, more specifically for the transport of a gas such as nitrogen or compressed air or for conveying a vacuum.
Such couplings are already known in the form of a sleeve-shaped hollow body with entrances for the pipes to be connected, whereby the entrances are provided with a radial seat with an end stop in which an aforementioned pipe end can be held, and whereby each entrance is provided with a coupling nut that fits around the pipe end to be connected and which can be tightened on the body in order to clamp a pipe end concerned in the coupling, whereby at least one gasket is provided between the coupling nut and the body, which is tensioned when the coupling nut is tightened in order to obtain a leak-free seal.
The pipes and couplings can be can made of metal, for example aluminium, provided with a protective coating or paint or otherwise, in which case the pipe system of the pipes coupled together sometimes have to be connected to an electrical earth.
When such pipes and couplings are used in an explosion-sensitive environment, for example when trading or transporting powdered bulk products, the pipe system of connected pipes and couplings must be earthed.
Indeed, when transporting liquids or gases through the pipes static electricity can be generated due to the friction between the gas or the liquid on the one hand, and the pipe system on the other, which can lead to the occurrence of sparks if the pipe system is not earthed.
However, the present couplings of the aforementioned type are generally made of a hard plastic, as such couplings can be produced more cheaply by injection moulding or similar, and such couplings are also insensitive to corrosion.
A problem that occurs here is that each plastic coupling forms an electrical break between two metal pipes coupled together.
This means that such a pipe system with plastic couplings cannot be used as an earth conductor and consequently a separate earth conductor has to be provided for the earthing.
The electrical break at the location of each plastic coupling also means that, in the event of explosion-sensitive conditions, each metal pipe has to be earthed separately to be able to conduct the generated static electricity away.
This means a substantial price increase as such earthing must be implemented with the necessary care in order to guarantee a sufficiently low electrical resistance of the earthing, which is required for good earthing.
A known but little applied solution is to connect the metal pipes together using an external electrical conductor to bridge the electrical break at the location of the couplings between the pipes.
However, this solution has the disadvantage that it requires further work after connecting two pipes together with a plastic coupling, i.e. an extra bridge has to be affixed across the coupling.
An additional disadvantage is that there must be facilities to be able to construct the bridge with the required low resistance. For example, the pipe surface must be prepared to be able to make a good electrical connection, for example by suitable cleaning for a bare metal pipe, and for a coated metal pipe by scraping or rubbing off the coating. Then the bridge must be affixed there by means of soldering, brazing, clamping or similar.
All this means extra costs in materials and working hours.
Another disadvantage of an external bridge is that it is exposed to the risk of accidental damage or sabotage, in which case an explosion hazard arises on account of inadequate earthing without it being discovered in time.